This section discusses objections to programmed aging theories raised by proponents of non-programmed theories. Programmed theories hold that organism designs purposely cause aging and limited life span. Non-programmed theories hold that aging results from fundamental limitations, results from the inability of the organism to better combat deteriorative processes, or is an accidental side-effect of some beneficial function.
Programmed theories provide a much better match to the totality of empirical evidence. This is a somewhat foregone conclusion because evolved mechanisms (e.g. those supporting mentation, locomotion, vision, etc.) are typically very complex. It is therefore easy to envision complex evolved life span regulation mechanisms that rather precisely match all of the observations (see Aging Mechanisms). Since, in the non-programmed theories, aging is essentially an accidental aspect of organism design, it is dramatically more difficult to explain how a complex coordinated mechanism could have evolved, or how an accidental design feature could match the observations. Recent discoveries of explicit aging mechanisms such as aging genes improve the case for programmed theories.
We can define traditional evolutionary mechanics theory as the idea that natural selection as taught in high school biology classes is the only factor that influences the evolution process. The main argument against programmed theories is that traditional theory prohibits programmed aging and that it is "impossible" that traditional "survival of the fittest" theory could be less than perfectly comprehensive. Consequently, any apparently conflicting evidence should be deprecated, discounted, or disregarded. A typical statement:
“The way evolution works makes it impossible for us to possess genes that are specifically designed to cause physiological decline with age or to control how long we live.” Olshansky, Hayflick, and Carnes, Scientific American, 2004 [ed note: aging genes in simple organisms were discovered in 1993 and were subsequently discovered in mammals.]
In effect, these theorists are suggesting that it is impossible that they do not have a perfect understanding of the evolution process. This position fits rather well with the perception of many people who have a relatively casual exposure to modern evolutionary mechanics concepts and also reflects ~1950 era scientific consensus. The current situation is that there is excellent scientific agreement based on very strong evidence that life on Earth has indeed evolved. There is also very good agreement based on strong evidence that traditional natural selection, is, at a minimum, the main factor influencing the evolution process.
However, there is currently substantial scientific disagreement as to whether various natural secondary effects also influence the evolution process. Proposals regarding such secondary effects now include group selection, kin selection, evolvability, gene-oriented selection, and effects of various genomic design characteristics on the evolution process. All of these additions to traditional theory logically allow programmed aging and specific programmed aging theories have been published based on most of them.
Traditional theory requires that evolved characteristics benefit the ability of individual organisms to survive or reproduce. All of the alternative theories expand this definition to include more diffuse benefits such as benefits to groups, small groups (kin), the evolution process (evolvability), or propagation of genes (e.g. selfish gene theory).
Since the secondary effects are, essentially by definition, weaker than natural selection, and because they typically operate over even longer time frames, experimental confirmation is even more difficult, the science is weaker, and theories tend to be relatively more philosophical and less scientific. Formal scientific arguments regarding the existence of and nature of the secondary effects have now extended at least since 1962. It is very important to note that the secondary theories were motivated by apparent discrepancies between observations and traditional theory other than aging and life span (see Problems with Evolution Theory). Some apparent discrepancies, especially concerning aging and life span, were noticed much earlier, ~1859!
Traditionalists point out that traditional theory has existed for 150 years and, without question, fits the vast majority of observations. Reformists point out that observed discrepancies have remained unresolved for 150 years and continue to accumulate. We do not reject relativistic physics merely because Newtonian physics has existed for 320 years and explains 99 percent of the observations.
A major traditional objection involves the sequence and scenario by which a mutational design change propagates and is retained in a population. How would a change that caused an individual disadvantage (e.g. shorter life span) without compensating individual advantage (such as to reproduction) propagate sufficiently as to result in a group or other long term benefit. Wouldn't such a change "select out" prior to the point at which the long-term benefit would be felt? Wouldn't "cheaters", not possessing the individually disadvantageous quality, have a propagation advantage? Is not a group advantage weaker and slower than an individual disadvantage? Indeed, traditionalists contend that the largest imaginable group advantage would be outweighed by the smallest possible individual disadvantage. Reformists suggest that an evolvability advantage is not slower or "longer-term" than an individual disadvantage. They also suggest that an individually disadvantageous but group benefiting characteristic could survive short-term out-selection by being rigidly linked to an individually beneficial characteristic. This exact argument was used to support a popular non-programmed (antagonistic pleiotropy) theory of aging! The gene-oriented theories and alternative theories based on genomic design use similar arguments. The term robustness is used to describe traits that resist the effects of natural selection because of such considerations.
Note that there is little objection to the idea that an organism characteristic could have a group or evolvability benefit nor to specific benefits of a design-limited life span suggested by programmed aging theories. The objection is to the idea that a group or evolvability benefit could outweigh an individual disadvantage in the selection process.
Major formal objections to alternative theories (such as G. Williams 1971 book Group Selection) are quite dated and were directed at group selection. Current proponents of traditional theory suggest that the much newer evolvability and genomic theories are similar to group selection and can be dismissed using the same arguments. Reformists contend that the later theories are logically quite different and not subject to the criticisms earlier directed at group selection.
Evolutionary theories of aging invoke evolutionary arguments in attempting to explain why an organism should age or have a limited life span and encompass both programmed and some non-programmed theories. Each of the evolutionary theories in turn depends on one or another concept regarding the evolutionary value of life. The value of life concepts upon which all of the popular non-programmed evolutionary theories such as the antagonistic pleiotropy theory, mutation accumulation theory, and disposable soma theory are constructed are themselves subject to the same problems as the evolutionary mechanics issues. They involve secondary effects, are difficult to experimentally demonstrate, conflict with traditional theory, and are consequently the subject of interminable scientific disagreement. In choosing an aging theory, one picks an evolutionary mechanics concept and then chooses a compatible value of life concept. Evolutionary theories of aging thus involve cascading a scientifically controversial evolutionary mechanics concept with a scientifically controversial value of life concept. The situation is rife with logical absurdities. Example: One of the most popular value of life concepts (Medawar's hypothesis) holds that the traditional fitness disadvantage of aging is zero. Is it possible to prove that a group or evolvability advantage of a limited life span can not overcome a zero disadvantage? Of course not.
Discussions of non-programmed theories by their proponents tend to involve substantial exclusion of contrary evidence. One can write a theory of human aging that ignores contrary observational evidence from other mammals. A theory of mammal aging can ignore contrary evidence from non-mammals as "irrelevant." The difficulty with this is that the underlying principles and assumptions are extremely broad in scope. For example, evolution theory is generally held to apply to all living organisms. The value of life concepts have a similarly broad basis. Therefore theories based on these broad principles should also be broadly applicable. Unless supported with a plausible rationale, exclusion of contrary evidence is scientifically unjustifiable.
In areas of inquiry where the science is relatively weak, non-science factors are proportionately more important in influencing scientific and popular thinking. These factors tend to create bias favoring non-programmed theories and traditional mechanics.
In view of the above discussion, it would appear that the logical scientific path would be to place more faith in direct observations vs. theories. In particular, it appears to be scientifically ridiculous to religiously believe and promote the idea that traditional mechanics theory is infallible despite all contrary evidence and scientific controversy while simultaneously accepting a controversial value of life concept.
The fundamental conundrum surrounding aging theories for 150 years is that explanations that do not depend on an evolutionary rationale grossly fail to match observations while explanations that do invoke evolutionary rationales become embroiled in endless semi-philosophical academic wrangling. Because aging theory has significant implications for medicine, we need to find a way out of this endless loop and finally solve the "unsolved problem of Biology!"
Sponsored by Azinet LLC © 2010